PCMCIA is an acronym for Personal Computer Memory Card International Association. This association developed a set of standards designed to make computer expansion easier. PCMCIA cards (also known as PC Cards) can be used, for example, to add memory or input/output capabilities to computers in credit card size packaging. These credit card sized expansion modules fit into a variety of computing products, including desktop and laptop computers.
Leading market research firms have indicated that by the year 1996 the number of users of pocket-size, hand-held and portable computing and communicating devices with the PCMCIA standard could escalate to nearly 10 million. There are basically three standard types of PCMCIA slots for these cards: Type I-(3 mm slot), Type II-(5 mm slot), and Type III-(10 mm slot). Various sized cards slide into appropriately sized slots much like a floppy disc fits into a drive.
PCMCIA cards generally comprise a credit card sized printed circuit board or substrate (PCB), having a number of integrated circuits and components soldered thereto. The PCMCIA card includes a connector soldered onto an edge thereof to interconnect with a host device. The interconnection between the circuitry of the PCMCIA card and the host device includes a pin and socket configuration. The PCMCIA connector for a Type II card, for example, comprises a configuration of 68 sockets or holes which are designed to electrically interface with mating 68 pins of a connector within the host device.
With these strict size standards, special considerations must be made in the selection of thin line and fine pitched components. Using these components in PCMCIA cards will require higher standards in the manufacturing process, including automation.
In the manufacturing of PCMCIA cards, the small size of the connector and the high number of electrical connections between the connector and the circuitry of the card itself makes precise manual placement of the connector onto the card a tedious and time consuming process. Manual placement increases the chance for defects due to misalignment or mishandling. A solution to this problem would be to provide an automated process of attaching the connector to the PCB.
A number of assembly problems arise during the placement and attachment of the PCB between the connector leads. First of all, as shown in FIG. 1, since the distance between the top connector leads 12 and bottom connector leads 14 is usually less than 0.02 inches (0.508 mm) in the straight leaded straddle-mount connectors 15 used in the industry, it is difficult to manually assemble and practically impossible to assemble in an automated process due to the likelihood of lead interference with the edge of the PCB 18 and the solder bump 20 during the attachment process.
A second type of connector available is the compression fit, straddle-mount connector 16 shown in FIG. 2. This type of connector 16 has a radius in the top leads 12 to accommodate angled insertion of the PCB 18 by providing a type of "lead in" ramp 11. The range of clearance when the connector is initially attached at a 22.5.degree. angle of attack is approximately 0.041 inches.+-.0.005 inches (1.0414 mm.+-.0.127 mm). This "angle of attack" insertion method aids in the assembly process by providing a larger target area decreasing the need for exact z-axis (vertical/up-down) alignment. However, this "lead-in" ramp 11 still requires nearly exact alignment, which is difficult to accomplish in an automated manufacturing process, since the range of clearance is only approximately 0.04 inches (1.016 mm).
A solution to this problem would be to provide a type of compression fit, straddle-mount connector which has a greater clearance to provide for easier automation.
Alignment problems also exist in the automated assembly of the cards. The edge of the PCB array onto which the connector is attached is usually straight with no accommodations for alignment in the x (horizontal/side-to-side), y (horizontal/front-to-back), or z (vertical/up-down) axes. A solution to this problem would be to provide a number of alignment mechanisms along each of the three axes to assist in overall alignment during the automated process.
Another problem arises with respect to the soldering process. During assembly, solder paste is generally applied to the PCB prior to attachment of the connector. Because of the close fit of the PCB between the leads, the solder paste is usually displaced due to driving the leads directly into the paste on the PCB leading to faults in the connection and shorts.
Furthermore, an x-axis (horizontal) warping problem arises in the pre-soldering of the PCB. Warping arises from various environments. Fabrication of the substrate material is one cause of warping. Even after the substrate has been leveled off, its memory elasticity from previous warping can cause warping again in the first reflow cycle.
A solution to this problem would be to provide a method of soldering which prevents this displacement of the solder paste and accommodates any warpage during the assembly process, resulting in precise and secure connections.
Thus, there is a need in the art for a method of automated attachment of the PCMCIA connector onto the PCB. This need includes a type of compression fit, straddle-mount connector which has a greater clearance to provide for easier automation and a number of alignment mechanisms along each of the three axes to assist in overall alignment of the connector onto the PCB during the automated assembly process. There is also a need for an improved solder paste screening method to avoid displacement of the solder paste which results in shorts.